早上git加星了webapp的教程

> h                                             => {}  ／／但并没有存入hash。仍然是空的。

h = Hash.new { |hash, key| hash[key] = "Go Fish: #{key}" }

创建一个空hash，设置了默认的value值,如：

h["c"] #=> "Go Fish: c"

hash存入key,value对儿，不再为空。

hash的Methods中有 比较的operation. < , <= , ==, > ,>=.

clear -> hsh: Removes all key-value pairs from hsh.

values → array :

Returns a new array populated with the values from hsh. 同理 h.keys 回传一个数组包含所以keys.

h = { "a" => 100, "b" => 200, "c" => 300 }

h.keys #=> ['a', 'b', 'c']

h.values #=> [100, 200, 300]

另外： h.valuse_at('a', 'b')     #=> [100, 200] 这是指定一组keys,回传一组【values】

Lenght -> integer

h = { "d" => 100, "a" => 200, "v" => 300, "e" => 400 } 

h.length #=> 4 

h.delete("a") #=> 200 

h.length #=> 3 

store(key, value) -> value

Associates the value given by value with the key given by key.

h = { "a" => 100, "b" => 200 }

h["a"] = 9

h["c"] = 4   //本来没有，于是新增一对kv值。

h   #=> {"a"=>9, "b"=>200, "c"=>4}

h.store("d", 42) #=> 42

h   #=> {"a"=>9, "b"=>200, "c"=>4, "d"=>42} 

 merge(other_hash) → new_hash

 merge(other_hash){|key, oldval, newval| block} → new_hash

Returns a new hash containing the contents of other_hash and the contents of hsh. If no block is specified, the value for entries with duplicate keys will be that of other_hash.

Otherwise the value for each duplicate key is determined by calling the block with the key, its value in hsh and its value in other_hash.

For example:

h1 = { "a" => 100, "b" => 200 }

h2 = { "b" => 254, "c" => 300 }

h1.merge(h2) #=> {"a"=>100, "b"=>254, "c"=>300}

h1.merge(h2){|key, oldval, newval| (newval - oldval)*2 }

 #=> {"a"=>100, "b"=>108, "c"=>300}

h1 #=> {"a"=>100, "b"=>200}

has_value?(value) → true or false

h = { "a" => 100, "b" => 200 }

h.has_key?("a")   #=> true

h.value?(100)   #=> true 
h.value?(999)   #=> false